Lactobacillus Reuteri Benefits: What Does It Do? The Trials

Lactobacillus reuteri is a species of live culture whose best evidence is in babies: in a 2024 pooled analysis of colic trials, one specific strain shortened crying by about an hour a day. In adults the record is smaller, and the best-known finding, less bone loss in older women over a year, comes from one trial that a larger two-year trial did not repeat. This page is one spoke of the Wellgard probiotics guide.

Evidence at a glance

• Trials: colic, two pooled analyses (one of 32 trials, 2,242 infants); bone, two trials of 90 and 239 women; gums, one trial of 30 adults.
• Largest single trial: 239 women aged 50 to 60, two years.
• Strongest measured outcome: daily crying time in colicky infants, 64.66 minutes less with the specific strain.
• Not tested in any trial we found: testosterone in adults; bone density in men.

Sources checked on 12 October 2026.

What is Lactobacillus reuteri?

Lactobacillus reuteri is a species of lactic acid bacteria found in the human gut, urinary tract, skin and breast milk, and in many other mammals.¹ In food it is a sourdough organism, present in some starters, and it is added by name to a few yoghurts and fermented milks.¹⁴ Since 2020 its formal name has been Limosilactobacillus reuteri: that year the genus Lactobacillus, then 261 species, was split into 25 genera on whole-genome evidence. The bacterium and its trials are unchanged.²

In the laboratory it makes antimicrobial compounds, including organic acids, ethanol and a molecule called reuterin, and some strains reduce pro-inflammatory signalling molecules while encouraging regulatory T cells.¹ Like other swallowed live cultures it does not settle for good: a 2015 review calls ingested lactobacilli a transient part of the microbiome.³

What are the benefits of Lactobacillus reuteri?

Infant colic. A 2024 pooled analysis of randomised trials in babies under three months found crying reduced by 51 minutes a day on average, 64.66 minutes with one specific L. reuteri strain and, across all cultures pooled, 74.28 minutes in exclusively breastfed babies; the evidence in formula-fed and caesarean-born babies is limited.⁴ A network analysis of 32 trials, 2,242 infants, ranked the same strain above the other interventions for crying time after 21 to 28 days.⁵ The NHS colic page, last reviewed April 2022 and past its review date, says of anti-colic drops and supplements: "they're not recommended and there's no evidence they help colic".⁶ Anything given to a baby goes through a health visitor or GP first.

Bone density in women. In a one-year trial of 90 women aged 75 to 80 with low bone density, the group taking a specific L. reuteri strain at 10 billion live cells a day lost 0.83% of shin-bone density against 1.85% on placebo, a difference of 1.02% (95% confidence interval 0.02 to 2.03); secondary bone measures did not reach significance and adverse events did not differ.⁷ The same centre then gave the same strain, at 500 million or 5 billion live cells twice daily with 200 IU of vitamin D in every capsule, to 239 women aged 50 to 60 for two years: shin-bone density fell in every group with no difference between them (high dose against placebo, -0.08%, 95% confidence interval -0.85 to 0.69), and the authors conclude it "had no effect on bone loss or bone turnover over 2 years".⁸

Gum disease. In one partly supplier-funded trial of 30 adults with chronic periodontitis, L. reuteri lozenges twice a day for 12 weeks alongside scaling and root planing gave more pocket-depth reduction and attachment gain in moderate and deep pockets than placebo (P < 0.05). A lozenge, not a swallowed capsule, was tested.⁹

Adult digestion. None of these trials measured bloating, bowel habit or digestive comfort in adults. Cholesterol, Helicobacter pylori and eczema claims in older sources have no consistent trial record we could find.

Does Lactobacillus reuteri have any side effects?

In the two bone trials adverse events did not differ from placebo over one and two years.^{7, 8} Across live cultures more broadly, 36 randomised trials in 9,312 adults on antibiotics, pooled, found no more adverse events than placebo (relative risk 1.00, 95% confidence interval 0.87 to 1.14).¹⁰ Mild wind or looser stools in the first days are the usual reports.

A systematic review in people with cancer, 17 studies and 1,530 people, found five case reports of bacteraemia or fungaemia and concluded that such products "may be a rare cause of sepsis".¹¹ Those reports cluster in people whose immune system is suppressed, including by chemotherapy, the critically ill, people with a central venous catheter or feeding line, and premature or hospitalised babies. The NHS page on live cultures, last reviewed November 2022 and past its review date, says anyone with an existing health condition or a weakened immune system should talk to a doctor first.¹² The full list is on who should take care with live cultures.

How long does it take for L. reuteri to work?

As long as the trial that measured the outcome you want: 21 to 28 days in the colic trials, 12 weeks in the gum trial, 12 months and two years in the bone trials.^{5, 7, 8, 9} For adult digestion no L. reuteri trial gives a timeline; the "3 to 4 days" quoted online is not from a trial.

After stopping, the data are for a different species: in 117 people dosed daily with a bifidobacterium strain for eight weeks, stool levels rose while it was taken and fell back towards baseline afterwards.¹³ No trial reports a rebound or a dependency.

Where does L. reuteri come from?

From people, from a few fermented foods and from labelled supplements. In people it lives in the gut, urinary tract, skin and breast milk.¹ In food it is a sourdough organism: in one industrial sourdough, strains producing its antibiotic reutericyclin were still present after ten years of continuous refreshing.¹⁴ Baking kills it. Yoghurts and fermented milks that list L. reuteri have had the strain added. The food list is on which foods contain Lactobacillus reuteri, and the home-yoghurt question on L. reuteri yoghurt.

The trials used one named strain at a stated daily count for a fixed period; a species-only label names the family, not the trial.

What we don't know

• No randomised trial has tested L. reuteri for bone density in men, or in women under 50.
• No human trial we could find has measured testosterone with L. reuteri; the only mood data come from a three-strain mix.¹⁵
• No trial has measured digestive comfort in healthy adults taking L. reuteri.
• No trial has settled whether the colic result holds in formula-fed or caesarean-born babies.⁴

Frequently asked questions

Is Lactobacillus reuteri good for women?

Both bone trials were in women: positive at 12 months in 90 women aged 75 to 80, null over two years in 239 women aged 50 to 60.^{7, 8} Questions about the intimate flora belong to what intimate flora is.

Is Lactobacillus reuteri good for babies?

In pooled colic trials one specific strain reduced daily crying by about an hour; across all cultures pooled, crying fell most in exclusively breastfed babies. The NHS colic page says there is no evidence such remedies help.^{4, 6} A health visitor or GP decides anything given to a baby.

Is Lactobacillus reuteri in yoghurt?

Only in yoghurts and fermented milks to which the strain has been added and named on the label.

Does Lactobacillus reuteri help with weight or testosterone?

The testosterone findings are from mice, as the 2018 bone trial notes; we found no human trial.⁷ On weight, two 12-week trials: one strain alone in 53 adults with metabolic syndrome (supplier-funded) changed none of its features against placebo,¹⁶ and a three-strain mix in 102 women with obesity reported weight and mood improving from baseline.¹⁵

Sources

1. Mu Q, Tavella VJ, Luo XM. Role of Lactobacillus reuteri in human health and diseases. Narrative review. Frontiers in Microbiology, 2018. PubMed 29725324.
2. Zheng J, et al. A taxonomic note on the genus Lactobacillus: description of 23 novel genera. Taxonomic study, 261 species. International Journal of Systematic and Evolutionary Microbiology, 2020. PubMed 32293557.
3. Derrien M, van Hylckama Vlieg JE. Fate, activity, and impact of ingested bacteria within the human gut microbiota. Review of clinical studies. Trends in Microbiology, 2015. PubMed 25840765.
4. Vaz SR, et al. Probiotics for infantile colic: is there evidence beyond doubt? Pooled analysis of randomised trials, infants under 3 months. Acta Paediatrica, 2024. PubMed 37962097.
5. Gutiérrez-Castrellón P, et al. Medicine, 2017. Network analysis of one Lactobacillus reuteri strain for infantile colic, 32 randomised trials, 2,242 infants. PubMed 29390535.
6. NHS. Colic. nhs.uk/conditions/colic. Page last reviewed 26 April 2022 (review overdue).
7. Nilsson AG, et al. Lactobacillus reuteri reduces bone loss in older women with low bone mineral density. Randomised trial, 90 women aged 75 to 80, 12 months. Journal of Internal Medicine, 2018. PubMed 29926979.
8. Gregori G, et al. JAMA Network Open, 2024. Randomised trial of one Limosilactobacillus reuteri strain and early postmenopausal bone loss, 239 women aged 50 to 60, 2 years. PubMed 38865129.
9. Teughels W, et al. Clinical and microbiological effects of Lactobacillus reuteri probiotics in the treatment of chronic periodontitis. Randomised trial, 30 adults, 12 weeks; partly supplier-funded. Journal of Clinical Periodontology, 2013. PubMed 24164569.
10. Liao W, et al. Probiotics for the prevention of antibiotic-associated diarrhea in adults. Pooled analysis, 36 randomised trials, 9,312 people. Journal of Clinical Gastroenterology, 2021. PubMed 33234881.
11. Redman MG, Ward EJ, Phillips RS. The efficacy and safety of probiotics in people with cancer: a systematic review. Systematic review, 17 studies, 1,530 people. Annals of Oncology, 2014. PubMed 24618152.
12. NHS. Probiotics. nhs.uk/conditions/probiotics. Page last reviewed 24 November 2022 (review overdue).
13. Charbonneau D, Gibb RD, Quigley EM. Gut Microbes, 2013. Stool-tracking study of one Bifidobacterium infantis strain, 117 people, 8 weeks. PubMed 23549409.
14. Gänzle MG, Vogel RF. Contribution of reutericyclin production to the stable persistence of Lactobacillus reuteri in an industrial sourdough fermentation. Laboratory study, one sourdough, 10 years. International Journal of Food Microbiology, 2003. PubMed 12430769.
15. Yin L, et al. Journal of Applied Microbiology, 2026. Randomised trial, three-strain mix, 102 women, 12 weeks. PubMed 42731127.
16. Tenorio-Jiménez C, et al. Nutrients, 2019. Randomised crossover trial, one strain, 53 adults, 12 weeks; supplier-funded. PubMed 31370223.

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